<?php
$a = array(1,2,array(3,4, array(5,6,7), 8), 9);
$b = call_user_func_array('array_merge', $a);
$c = array();
$it = new RecursiveIteratorIterator(new RecursiveArrayIterator($a));
foreach($it as $v) {
$c[] = $v;
}
print_r($a);
print_r($b);
print_r($c);
print_r($it);